This invention relates to an improved oil shale retorting process and a separation system for removing rock solids from heat-carrier solids which are cycled in the retorting process. The rock solids are removed in a gas fluidized classifier especially useful for the relationship between rock solids and heat-carrier solids.
It has been proposed to use heat-carrying spherically-shaped solids to retort the solid carbonaceous organic matter (commonly called kerogen) in oil shale to produce petroleum products. The spherically-shaped solids are heated and these hot heat carriers are mixed with crushed oil shale. The heat from the hot heat-carrying solids helps to convert the kerogen in the oil shale to oil and gas and produces a mixture of heat-carrier solids and spent shale solids. The heat-carrier solids of a significant size are separated from the spent shale solids so that the heat-carrier solids may be heated and cycled through the retorting process. In a process of the type described in U.S. Pat. No. 3,844,929, the heat-carrying solids are special porous pellets having a surface area of at least 10 square meters per gram and a size ranging from approximately 0.04 centimeter (0.055 inch) to approximately 1.27 centimeters (0.5 inch). In this process, a combustible deposition is formed on the pellets. This deposition is burned to reheat the pellets. In the process, it is especially important that the pellets are recovered from the spent shale and that only a small amount of spent shale be retained with the pellets. In U.S. Pat. No. 3,803,021, a combination elutriation-size screening separating system is provided. In co-pending application Ser. No. 749,505, filed Dec. 10, 1976 and now U.S. Pat. No. 4,118,309, entitled "Separation and Recovery of Heat Carriers in an Oil Shale Retorting Process," and owned by a common assignee, a continuously restored inclined surface is provided for assisting in separation of heat-carrier solids from the spent shale solids.
For the most part, the previously suggested separating processes will remove 95 percent or more of the undesired spent shale solids. The remaining spent shale solids contain rock solids. Some of the remaining rock solids will disintegrate on being cycled through the retorting process. But some of the remaining rock solids are not disintegrated and this type of rock solids will accumulate in the system if they are not removed. These rock solids are a hard, temperature resistant, spherically-shaped gravel-like rock which are difficult to remove by the previously suggested systems.